This invention relates to improvements in a discharge surface treatment electrode and a manufacturing method thereof and a discharge surface treatment method used for discharge surface treatment for causing discharge to occur between the electrode and a workpiece and forming a hard film made of electrode material on the workpiece surface by the discharge energy or a hard film made of a substance resulting from the electrode material reacting with by the discharge energy on the workpiece surface.
Hitherto, a discharge surface treatment method, for example, disclosed in JP-A-5-148615 has been available as an art of forming a hard film on a workpiece surface for providing corrosion resistance and abrasion resistance. This art provides a discharge surface treatment method of metal material consisting of two steps of performing primary working (laying-up working) using a compacted powder electrode of a discharge surface treatment electrode comprising WC (tungsten carbide) powder and Co (cobalt) powder mixed and compressed and molded and then replacing the electrode with an electrode comparatively less quickly consumed such as a copper electrode and performing secondary working (re-melt working). This method can form a hard film having strong adhesion to a copper material, but is difficult to form a hard film having strong adhesion to a sintered material such as a hard alloy.
However, our study finds out that if a material for forming hard carbide such as Ti (titanium) is used as a discharge surface treatment electrode and discharge is caused to occur between the electrode and a metal material of a workpiece, a hard film can be formed on the metal surface of the workpiece without a re-melt step. The reason why a strong hard film can be formed is that with the discharging, the consumed electrode material and C (carbon) of a component of work liquid react with each other to produce TiC (titanium carbide). It is also found out that if discharge is caused to occur between a compacted powder electrode of a discharge surface treatment electrode made of metal hydride such as TiH2 (titanium hydride) and a metal material of a workpiece, a hard film can be formed more rapidly and with higher adhesion as compared with the case where Ti etc. is used as the material. Further, it is found out that if discharge is caused to occur between a compact powder electrode of a discharge surface treatment electrode comprising any other metal or ceramics mixed with hydride such as TiH2 and a metal material of a workpiece, a hard film having various properties of hardness, abrasion resistance, etc., can be formed more quickly.
Such a method is disclosed, for example, in JP-A-192937/1997. A configuration example of a discharge surface treatment electrode and an apparatus used for such discharge surface treatment will be discussed with reference to FIG. 7. In the figure, numeral 1 denotes a compacted powder electrode of a discharge surface treatment electrode comprising TiH2 powder compressed and molded, numeral 2 denotes a workpiece, numeral 3 denotes a work tank, numeral 4 denotes work liquid, numeral 5 denotes a switching element for switching voltage and current applied to the compact powder electrode 1 and the workpiece 2, numeral 6 denotes a control circuit for controlling turning on/off the switching element 5, numeral 7 denotes a power supply, numeral 8 denotes a resistor, and numeral 9 denotes a formed hard film. According to such a configuration, discharge is caused to occur between the compact powder electrode 1 and the workpiece 2 and the hard film 9 can be formed by the discharge energy on the surface of the workpiece 2 made of steel, a hard alloy, etc.
Such formation of a hard film made of carbide, etc., on a workpiece by discharge surface treatment is executed by forming a film of carbide on the workpiece by heat energy of discharge using the carbide which becomes the component of the hard film to be formed as a component of the discharge surface treatment electrode or by using metal containing the carbide which becomes a component of the hard film to be formed or a compound of that metal as the component of the discharge surface treatment electrode and causing the metal or the metal compound to react with a component of work liquid, C, by heat energy of discharge to form a hard film made of carbide on the workpiece.
Here, if the component of the discharge surface treatment electrode is only a material having comparatively high hardness such as carbide, powder of the discharge surface treatment electrode component cannot be fixed by compression molding of press and thus usually a material having comparatively low hardness is mixed as a binder. However, if Co (cobalt), etc., used as a binder to manufacture a sintered alloy, etc., is mixed as an electrode material, it is a material not producing carbide and thus the hardness of a hard film formed on a workpiece becomes low and the material cannot be used for such application where high abrasion resistance is required; this is a problem. Some materials in the hard film formed on the workpiece may be poor in compatibility with the base material of the workpiece and in such a case, there is a problem of weakening the adhesive strength of the hard film.
It is an object of the invention to solve the above-mentioned problems and provide a discharge surface treatment electrode and a manufacturing method thereof and a discharge surface treatment method capable of enhancing the hardness and strength of a hard film formed on a workpiece by discharge surface treatment.
According to the invention, there is provided a discharge surface treatment electrode used for discharge surface treatment causing discharge to occur between the electrode and a workpiece in work liquid containing carbon and forming a hard film containing metal carbide as a component on the surface of the workpiece by discharge energy, wherein the metal carbide and metal contained in the metal carbide or a compound of that metal or any other metal forming the hard carbide or a compound of that metal are contained as material of the discharge surface treatment electrode.
The metal carbide is metal carbide of metal or a metal compound contained in material of the workpiece.
The material of the discharge surface treatment electrode contains WC and W.
According to the invention, there is provided a manufacturing method of a discharge surface treatment electrode used for discharge surface treatment causing discharge to occur between the electrode and a workpiece in work liquid containing carbon and forming a hard film containing metal carbide as a component on a surface of the workpiece by discharge energy, wherein powder of the metal carbide and powder of metal contained in the metal carbide or powder of a compound of the metal or powder of any other metal forming hard carbide or powder of a compound of the metal are mixed and are compressed and molded to form the discharge surface treatment electrode.
Wax is added to the material of the discharge surface treatment electrode and then they are compressed and molded and are heated at a temperature at least as high as that at which the wax is melted and no higher than the temperature at which the wax is decomposed to produce soot, for evaporating and removing the wax to form the discharge surface treatment electrode.
According to the invention, there is provided a discharge surface treatment method for causing discharge to occur between a discharge surface treatment electrode and a workpiece in work liquid containing carbon and forming a hard film containing metal carbide as a component on the surface of the workpiece by discharge energy, wherein a discharge surface treatment electrode containing the metal carbide and metal contained in the metal carbide or a compound of that metal or any other metal forming hard carbide or a compound of that metal is used.
The metal carbide is metal carbide of metal or a metal compound contained in material of the workpiece.
The invention is configured as described above and thus has the advantage that the hardness and strength of a hard film formed on a workpiece by the discharge surface treatment can be enhanced.